全文获取类型
收费全文 | 2345篇 |
免费 | 194篇 |
出版年
2023年 | 4篇 |
2022年 | 10篇 |
2021年 | 33篇 |
2020年 | 11篇 |
2019年 | 14篇 |
2018年 | 26篇 |
2017年 | 25篇 |
2016年 | 38篇 |
2015年 | 108篇 |
2014年 | 94篇 |
2013年 | 117篇 |
2012年 | 181篇 |
2011年 | 161篇 |
2010年 | 112篇 |
2009年 | 114篇 |
2008年 | 145篇 |
2007年 | 159篇 |
2006年 | 145篇 |
2005年 | 133篇 |
2004年 | 149篇 |
2003年 | 168篇 |
2002年 | 124篇 |
2001年 | 34篇 |
2000年 | 12篇 |
1999年 | 39篇 |
1998年 | 40篇 |
1997年 | 33篇 |
1996年 | 24篇 |
1995年 | 33篇 |
1994年 | 27篇 |
1993年 | 23篇 |
1992年 | 19篇 |
1991年 | 20篇 |
1990年 | 9篇 |
1989年 | 22篇 |
1988年 | 17篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 6篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 8篇 |
1979年 | 4篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有2539条查询结果,搜索用时 15 毫秒
171.
Marker-free transgenic plants through genetically programmed auto-excision 总被引:4,自引:0,他引:4
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We present here a vector system to obtain homozygous marker-free transgenic plants without the need of extra handling and within the same time frame as compared to transformation methods in which the marker is not removed. By introducing a germline-specific auto-excision vector containing a cre recombinase gene under the control of a germline-specific promoter, transgenic plants become genetically programmed to lose the marker when its presence is no longer required (i.e. after the initial selection of primary transformants). Using promoters with different germline functionality, two modules of this genetic program were developed. In the first module, the promoter, placed upstream of the cre gene, confers CRE functionality in both the male and the female germline or in the common germline (e.g. floral meristem cells). In the second module, a promoter conferring single germline-specific CRE functionality was introduced upstream of the cre gene. Promoter sequences used in this work are derived from the APETALA1 and SOLO DANCERS genes from Arabidopsis (Arabidopsis thaliana) Columbia-0 conferring common germline and single germline functionality, respectively. Introduction of the genetic program did not reduce transformation efficiency. Marker-free homozygous progeny plants were efficiently obtained, regardless of which promoter was used. In addition, simplification of complex transgene loci was observed. 相似文献
172.
Three-dimensional pore space quantification of apple tissue using X-ray computed microtomography 总被引:1,自引:0,他引:1
The microstructure and the connectivity of the pore space are important variables for better understanding of the complex
gas transport phenomena that occur in plant tissues. In this study, we present an experimental procedure for image acquisition
and image processing to quantitatively characterize in 3D the pore space of apple tissues (Malus domestica Borkh.) for two cultivars (Jonagold and Braeburn) taken from the fleshy part of the cortex using X-ray computer microtomography.
Preliminary sensitivity analyses were performed to determine the effect of the resolution and the volume size (REV, representative
elementary volume analysis) on the computed porosity of apple samples. For comparison among cultivars, geometrical properties
such as porosity, specific surface area, number of disconnected pore volumes and their distribution parameters were extracted
and analyzed in triplicate based on the 3D skeletonization of the pore space (medial axis analysis). The results showed that
microtomography provides a resolution at the micrometer level to quantitatively analyze and characterize the 3D topology of
the pore space in apple tissue. The computed porosity was confirmed to be highly dependent of the resolution used, and the
minimum REV of the cortical flesh of apple fruit was estimated to be 1.3 mm3. Comparisons among the two cultivars using a resolution of 8.5 μm with a minimum REV cube showed that in spite of the complexity
and variability of the pore space network observed in Jonagold and Braeburn apples, the extracted parameters from the medial
axis were significantly different (P-value < 0.05). Medial axis parameters showed potential to differentiate the microstructure between the two evaluated apple
cultivars. 相似文献
173.
174.
Müller P Ewers C Bertsche U Anstett M Kallis T Breukink E Fraipont C Terrak M Nguyen-Distèche M Vollmer W 《The Journal of biological chemistry》2007,282(50):36394-36402
Bacterial cell division requires the coordinated action of cell division proteins and murein (peptidoglycan) synthases. Interactions involving the essential cell division protein FtsN and murein synthases were studied by affinity chromatography with membrane fraction. The murein synthases PBP1A, PBP1B, and PBP3 had an affinity to immobilized FtsN. FtsN and PBP3, but not PBP1A, showed an affinity to immobilized PBP1B. The direct interaction between FtsN and PBP1B was confirmed by pulldown experiments and surface plasmon resonance. The interaction was also detected by bacterial two-hybrid analysis. FtsN and PBP1B could be cross-linked in intact cells of the wild type and in cells depleted of PBP3 or FtsW. FtsN stimulated the in vitro murein synthesis activities of PBP1B. Thus, FtsN could have a role in controlling or modulating the activity of PBP1B during cell division in Escherichia coli. 相似文献
175.
Mainardi JL Hugonnet JE Rusconi F Fourgeaud M Dubost L Moumi AN Delfosse V Mayer C Gutmann L Rice LB Arthur M 《The Journal of biological chemistry》2007,282(42):30414-30422
The beta-lactam antibiotics mimic the D-alanyl(4)-D-alanine(5) extremity of peptidoglycan precursors and act as "suicide" substrates of the DD-transpeptidases that catalyze the last cross-linking step of peptidoglycan synthesis. We have previously shown that bypass of the dd-transpeptidases by the LD-transpeptidase of Enterococcus faecium (Ldt(fm)) leads to high level resistance to ampicillin. Ldt(fm) is specific for the L-lysyl(3)-D-alanine(4) bond of peptidoglycan precursors containing a tetrapeptide stem lacking D-alanine(5). This specificity was proposed to account for resistance, because the substrate of Ldt(fm) does not mimic beta-lactams in contrast to the D-alanyl(4)-D-alanine(5) extremity of pentapeptide stems used by the DD-transpeptidases. Here, we unexpectedly show that imipenem, a beta-lactam of the carbapenem class, totally inhibited Ldt(fm) at a low drug concentration that was sufficient to inhibit growth of the bacteria. Peptidoglycan cross-linking was also inhibited, indicating that Ldt(fm) is the in vivo target of imipenem. Stoichiometric and covalent modification of Ldt(fm) by imipenem was detected by mass spectrometry. The modification was mapped into the trypsin fragment of Ldt(fm) containing the catalytic Cys residue, and the Cys to Ala substitution prevented imipenem binding. The mass increment matched the mass of imipenem, indicating that inactivation of Ldt(fm) is likely to involve rupture of the beta-lactam ring and acylation of the catalytic Cys residue. Thus, the spectrum of activity of beta-lactams is not restricted to transpeptidases of the DD-specificity, as previously thought. Combination therapy with imipenem and ampicillin could therefore be active against E. faecium strains having the dual capacity to manufacture peptidoglycan with transpeptidases of the LD- and DD-specificities. 相似文献
176.
177.
178.
Identification of the L,D-transpeptidases responsible for attachment of the Braun lipoprotein to Escherichia coli peptidoglycan
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Magnet S Bellais S Dubost L Fourgeaud M Mainardi JL Petit-Frère S Marie A Mengin-Lecreulx D Arthur M Gutmann L 《Journal of bacteriology》2007,189(10):3927-3931
The L,D-transpeptidase Ldt(fm) catalyzes peptidoglycan cross-linking in beta-lactam-resistant mutant strains of Enterococcus faecium. Here, we show that in Escherichia coli Ldt(fm) homologues are responsible for the attachment of the Braun lipoprotein to murein, indicating that evolutionarily related domains have been tailored to use muropeptides or proteins as acyl acceptors in the L,D-transpeptidation reaction. 相似文献
179.
Recombining population structure of Plesiomonas shigelloides (Enterobacteriaceae) revealed by multilocus sequence typing
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Salerno A Delétoile A Lefevre M Ciznar I Krovacek K Grimont P Brisse S 《Journal of bacteriology》2007,189(21):7808-7818
Plesiomonas shigelloides is an emerging pathogen that is widespread in the aquatic environment and is responsible for intestinal diseases and extraintestinal infections in humans and other animals. Virtually nothing is known about its genetic diversity, population structure, and evolution, which severely limits epidemiological control. We addressed these questions by developing a multilocus sequence typing (MLST) system based on five genes (fusA, leuS, pyrG, recG, and rpoB) and analyzing 77 epidemiologically unrelated strains from several countries and several ecological sources. The phylogenetic position of P. shigelloides within family Enterobacteriaceae was precisely defined by phylogenetic analysis of the same gene portions in other family members. Within P. shigelloides, high levels of nucleotide diversity (average percentage of nucleotide differences between strains, 1.49%) and genotypic diversity (64 distinct sequence types; Simpson's index, 99.7%) were found, with no salient internal phylogenetic structure. We estimated that homologous recombination in housekeeping genes affects P. shigelloides alleles and nucleotides 7 and 77 times more frequently than mutation, respectively. These ratios are similar to those observed in the naturally transformable species Streptococcus pneumoniae with a high rate of recombination. In contrast, recombination within Salmonella enterica, Escherichia coli, and Yersinia enterocolitica was much less frequent. P. shigelloides thus stands out among members of the Enterobacteriaceae. Its high rate of recombination results in a lack of association between genomic background and O and H antigenic factors, as observed for the 51 serotypes found in our sample. Given its robustness and discriminatory power, we recommend MLST as a reference method for population biology studies and epidemiological tracking of P. shigelloides strains. 相似文献
180.
Olagnier D Costes P Berry A Linas MD Urrutigoity M Dechy-Cabaret O Benoit-Vical F 《Bioorganic & medicinal chemistry letters》2007,17(22):6075-6078
Pure natural monoterpenes were evaluated in vitro for their antiplasmodial activities against Plasmodium falciparum. Chemically modified terpenes were also tested to see whether the introduction of an alkyne, a cyclopropane, a diene, or a cyclopentenone moiety had an influence on the biological activity. The IC(50) obtained on a chloroquine-resistant strain of Plasmodium (FcM29-Cameroon) showed moderate activity, but with the alkyne and the cyclopentenone derivatives showing a promising enhancement of activity compared with the parent molecules. On the contrary, no antifungal activity was found in vitro using Candida albicans. Given the observed antiplasmodial activity of some of these modified monoterpenes, new monoterpene derivatives could be the basis for new antimalarial drugs to be researched. 相似文献